equirectangular.glsl

uniform samplerCube cubemap;

uniform float aperture;

varying vec4 vertTexCoord;

const float PI = 3.1415926535897932384626433832795;
const float DEG_TO_RAD = PI/180;

void main() {
  vec2 thetaphi = ((vertTexCoord.xy * 2.0) - vec2(1.0)) * vec2(PI, PI/2);

  vec3 rayDirection = vec3(cos(thetaphi.x), tan(aperture* DEG_TO_RAD)*thetaphi.y, sin(thetaphi.x));

  vec3 color = vec3(textureCube(cubemap, rayDirection));

  gl_FragColor = vec4(color, 1.0);
}